This study proposes to analyze surveys of nationally representative samples of office-based physicians conducted over a 22-year period (1973- 1994). The study aims to address the following major questions: 1. What do practitioners of adult primary care do in office-based practice? 2. How has the practice of office-based primary care changed over time? 3. To what extent is the practice of adult primary care influenced by environmental, patient-related, and physician factors, such as the characteristics of the local health care system, the supply of physicians, and patient ethnicity? 4. What are the implications of answers to questions 1-3 for public policy generally, and for training primary care practitioners in particular? The primary source of data will be the National Ambulatory Medical Care Surveys (NAMCS) from 1973, 1974, 1975, 1976, 1977, 1978, 1979, 1980, 1981, 1985, 1989, 1990, 1991, 1992, 1993 and 1994. NAMCS is conducted by the National Center for Health Statistics. Data from the 1991-92 NAMCS will be linked to elements from the 1992 Area Resources File maintained by the Bureau of Health Professions. NAMCS provide the most complete and detailed information now available concerning the characteristics of visits to office-based physicians, including patients' diagnoses and presenting complaints, duration of visit, tests and treatments provided, and referral and hospitalization decisions. These visit characteristics will be analyzed, over time and as a function of environmental, physician, practice organization, and patient characteristics. Techniques of exploratory and confirmatory data analysis will be used to explore a number of policy-relevant questions and hypotheses. The unique dataset available from NAMCS has never before been used for the purposes proposed here. Analyses will help to improve the training of practitioners of adult primary care, to inform efforts to make the practice of primary care more attractive, and to predict the effects on primary care of changes in the organization and financing of health care services.